Washington -LRB- CNN -RRB- -- In a dramatic slap at congressional authority , a divided Supreme Court has struck down a key part of a law that denies to legally married same-sex couples the same federal benefits provided to heterosexual spouses .

The Defense of Marriage Act defines marriage as only between a man and a woman .

The vote Wednesday was 5-4 .

`` Although Congress has great authority to design laws to fit its own conception of sound national policy , it can not deny the liberty protected by the Due Process Clause of the Fifth Amendment , '' said Justice Anthony Kennedy . He was supported by four more liberal colleagues : Justices Ruth Bader Ginsburg , Stephen Breyer , Sonia Sotomayor and Elena Kagan .

Read the ruling

The case examined whether the federal government can deny tax , health and pension benefits to same-sex couples in states where they can legally marry . At issue was whether DOMA violates equal protection guarantees in the Fifth Amendment 's due process clause as applied to same-sex couples legally married under the laws of their states .

The key plaintiff is Edith `` Edie '' Windsor , 84 , who married fellow New York resident Thea Spyer in Canada in 2007 , about 40 years into their relationship . By the time Spyer died in 2009 , New York courts recognized same-sex marriages performed in other countries .

But the federal government did n't recognize Windsor 's same-sex marriage , and she was forced to assume an estate tax bill much larger than those that other married couples would have to pay . So , Windsor sued the federal government .

A federal appeals court last year ruled in Windsor 's favor , saying DOMA violated the Constitution 's equal protection clause .

`` Today 's DOMA ruling is a historic step forward for #MarriageEquality . #LoveIsLove , '' President Barack Obama 's official Twitter account posted soon after the decision was handed down .

Kennedy , in his opinion , used sweeping language to affirm the rights of gays and lesbians .

`` For same-sex couples who wished to be married , the state -LRB- of New York -RRB- acted to give their lawful conduct a lawful status . This status is a far-reaching legal acknowledgment of the intimate relationship between two people , a relationship deemed by the state worthy of dignity in the community equal with all other marriages , '' he said . `` DOMA seeks to injure the very class New York seeks to protect . ''

But Kennedy -- a moderate-conservative who proved once again to be the `` swing , '' or deciding , vote -- made clear the ruling is limited : `` This opinion and its holding are confined to those lawful marriages . '' Thirty-five states have laws banning same-sex marriage .

Key quotes from the ruling

Under DOMA , Social Security , pension and bankruptcy benefits , along with family medical leave protections and other federal provisions , did not apply to gay and lesbian couples legally married in states that recognize such unions .

In a thunderous dissent , read from the bench , Justice Antonin Scalia slammed the majority for its `` exalted conception of the role of this institution '' -- the Supreme Court -- `` in America . ''

`` Few public controversies touch an institution so central to the lives of so many , and few inspire such attendant passion by good people on both sides , '' he said . `` Few public controversies will ever demonstrate so vividly the beauty of what our -LRB- Constitution -RRB- framers gave us , a gift the court pawns today to buy its stolen moment in the spotlight : a system of government that permits us to rule ourselves . ''

Scalia added , `` Some will rejoice in today 's decision , and some will despair at it ; that is the nature of a controversy that matters so much to so many . But the court has cheated both sides , robbing the winners of an honest victory , and the losers of the peace that comes from a fair defeat . We owed both of them better . I dissent . ''

Chief Justice John Roberts and Justices Clarence Thomas and Samuel Alito also dissented .

Windsor was in New York when the ruling came down . She told reporters that she was overjoyed .

`` We won everything we asked and hoped for . Wow , '' she said . `` I 'm honored and humbled and overjoyed to be here today to represent not only the thousands of Americans whose lives have been adversely impacted by the Defense of Marriage Act , but those whose hopes and dreams have been constricted by the same discriminatory law . ''

Marrying for the benefits

Windsor thanked the supporters who cheered her on throughout the case .

`` Because of today 's Supreme Court ruling , the federal government can no longer discriminate against the marriages of gay and lesbian Americans . Children born today will grow up in a world without DOMA , and those same children who happen to be gay will be free to love and get married as Thea and I did , but with the same federal benefits , protections and dignity as everyone else , '' Windsor said . `` If I had to survive Thea , what a glorious way to do it . And she would be so pleased . ''

The Defense of Marriage law was defended in the high court by House Republicans , after Obama concluded the law was unconstitutional .

Traditionally , that role would fall to the solicitor general 's office . But president ordered Attorney General Eric Holder not to defend DOMA in court . That raised the question of whether any party could rightfully step in and defend the law .

By striking down the DOMA provision , the court decided the standing question was not at play in this case , and it had jurisdiction to decide the larger questions .

A bill known as the Respect for Marriage Act is working its way through Congress and would repeal DOMA .

That law does not prohibit states from allowing same-sex marriages , but it also does not force states to recognize such marriages performed in other states . Most of the current plaintiffs are federal workers , who are not allowed to add their spouses to health care plans and other benefits .

After historic rulings , what 's next ?

The case is U.S. v. Windsor -LRB- 12-307 -RRB- .

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NEW : Edith Windsor , who sued the federal government , says she is overjoyed by the ruling

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In a 5-4 decision , the high court says Congress can not deny equal protection

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`` Today 's DOMA ruling is a historic step forward , '' president 's twitter account posts

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Justice Antonin Scalia issues a thunderous dissent saying '' the court has cheated both sides ''